A standard drill chuck has a chuck body centered on an axis and formed on the axis with a rearwardly open hole or other formation adapted for engagement by a spindle or the like of a drive unit, and with a plurality of forwardly open angled guides adapted to receive respective jaws for gripping a tool at a front end of the chuck body. The jaws have outer edges formed with teeth that mesh with an internal screwthread of a tightening ring rotatable on the body about the axis and constrained against axial movement relative to the body so that, when the tightening ring is rotated, the jaws are moved forward to grip the tool or backward to release it. As a rule the tightening ring is received in a groove whose front flank is formed by a rearwardly directed shoulder of the chuck body and whose rear flank is formed by a roller bearing in turn bearing axially backward on a forwardly directed shoulder of the chuck body.
To tighten or loosen the chuck the standard procedure is for the user to grip the tightening ring or a sleeve attached to it so as to prevent it from rotating, and then actuated the drill's power unit to rotate the chuck body in the appropriate direction, thereby either advancing or retracting the jaws. The jaw teeth are normally formed between forward and rearwardly directed shoulders of the jaws and, when a front or rear end position is reached, the respective shoulder bottoms on the tightening ring or associated structure to prevent further rotation and movement.
The problem with this structure is that it is possible to wedge or jam the chuck, forcing the parts into such tight engagement with each other that subsequent rotation in the opposite direction is very difficult. Furthermore such bottoming out of the parts on each other at the end of a tightening or, more likely, a loosening operation can lead to substantial strain on and wear of the engaging parts.